After causing quite a stir at their first introduction, full-body scanners are expanding to airports across the country with little fanfare.

Chicago's Midway Airport will be one of 28 airports to receive the next round of body scanners. Chicago's O'Hare Airport got their scanners in the spring, along with ten other airports nationwide.

When the scanners were first introduced, they generated a great deal of controversy as privacy groups worried about TSA screeners seeing naked images of travelers' bodies. The scanners generate an X-ray image that penetrates clothing, creating a detailed image of the traveler's body--even male genitals.

They were implemented as a response to the attempted Christmas Day bombing of an aircraft, in which Umar Farouk Abdulmutallab allegedly smuggled explosives onto a plane in his underwear. The chemicals he smuggled on board failed to detonate.

But the brouhaha has been largely silenced since the scanners went into effect at some of America's largest airports earlier this year. With a few exceptions, their implementation has been without incident.

Now, the Obama administration is set to expand the scanners to a second tier of airports. Chicago's Midway will be one of the airports in the new wave.

The Chicago Tribune reports that Transportation Security Administration spokesperson Ann Davis said that the scanners should arrive "sometime this year."

TSA officials have responded to privacy critics by insisting that images from the machines do not look like photographs, and that passengers can opt for a pat-down instead of the Millimeter Wave screening.